A Bipolar Junction Transistor (BJT) is a three-terminal device which consists of two pn-junctions formed by sandwiching either p-type or n-type semiconductor material between a pair of opposite type semiconductors.The primary function of BJT is to increase the strength of a weak signal, i.e., it acts as an amplifier. A BJT can also be used as a solid state switch in electronic circuits.Types of BJTThere are two types of BJTs −NPN TransistorPNP TransistorIn this article, we will discuss in detail the working principle of both these types of BJTs.NPN TransistorAn npn-transistor is composed of two n-type semiconductor materials which are ... Read More

ATM is a connection-oriented network at a point where the sender or user which access devices are known as end-point, these end-points connected through a user to network interface (UNI) to the switches on the network, these switches provide a network to network interface (NNI).The architecture of the ATM is shown in the figure below.ATM transfers the information through a transmission path which is made up of a logical virtual path and virtual channel. The transmission path consists of the physical cable, which is connected to an ATM switch. The cables have a transfer speed of up to 155 megabits ... Read More

An ultimate form of multiplexing used in parts of the cellular telephone system and for some satellite communication is called Code Division Multiplexing (CDM). The specific version of CDM used in cell phones is called Code Division Multi-Access (CDMA).CDM does not rely on physical properties, including frequency or time. It can depend on an interesting numerical idea such as values from orthogonal vector spaces can be merged and separated without interference. The specific form used in the telephone network is the easiest to learn. Each sender is created a unique binary code Ci that is called chip sequence.Chip sequences are ... Read More

A transmission system is classified as asynchronous if the system enables the physical channel to be useless for an arbitrary time between two transmissions. The asynchronous design of communication is well-appropriated to applications that create data at random (e.g., a user classifying on a keyboard or a user that press on a link to include a web page, reads for a while, and then press on a link to include another page).The drawback of asynchrony improves from the lack of coordination between sender and receiver while the channel is empty. A receiver cannot know how long the channel will remain ... Read More

The alternative to parallel transmission, called serial transmission, sends one bit at a time. With the importance of speed, it may seem that anyone designing a data communications system would choose parallel transmission. However, most communication systems use serial mode.Following are the two main reasons for serial transmission−First, serial networks can be continued over long distances at much less cost because fewer physical wires are required, and intermediate electronic elements are less cheap.Second, using only one physical wire defines that there are never timing issues caused by one wire being slightly higher than another (a difference of millimetres can be ... Read More

To establish a reliable service between two machines on a network, transport protocols are implemented, which somehow resembles the data link protocols implemented at layer 2. The major difference lies in the fact that the data link layer uses a physical channel between two routers while the transport layer uses a subnet.Following are the issues for implementing transport protocols−Types of ServiceThe transport layer also determines the type of service provided to the users from the session layer. An error-free point-to-point communication to deliver messages in the order in which they were transmitted is one of the key functions of the ... Read More

FDDI stands for Fiber Distributed Data Interface. It is a collection of ANSI and ISO standards for data transmission on fiber-optic lines in a local area network (LAN) that can broaden in the range up to 200 km (124 miles). The FDDI protocol depends on the token ring protocol.FDDI cabling consists of two fiber rings, one transmitting clockwise and the other transmitting counterclockwise. Fiber Distributed Data Interface (FDDI) is generally implemented as a dual token-passing ring within a ring topology (for campus networks) or star topology (inside a building). The dual ring includes a primary and secondary ring.The primary ring ... Read More

The error-reporting message defines that the router encounters a problem when it processes an IP packet, then it reports a message. Error messages are continually transmitted to the original source because the only data possible in the datagram around the route is the source and destination IP addresses.The error reporting messages are generally classified into the following types−When a router cannot route a datagram, or a host cannot transfer a datagram, the datagram is rejected, and the router or the host share a destination-unreachable message back to the source host that proposed the datagram.Destination unreachable messages with codes 2 or ... Read More

The ICMP represents Internet Control Message Protocol. It is a network layer protocol. It can be used for error handling in the network layer, and it is generally used on network devices, including routers. IP Protocol is a best-effect delivery service that delivers a datagram from its original source to its final destination. It has two deficiencies−Lack of Error ControlLack of assistance mechanismsIP protocol also lacks a structure for host and management queries. A host needs to resolve if a router or another host is alive, and sometimes a network manager needs information from another host or router.ICMP has been ... Read More

Reverse Address Resolution Protocol (RARP) is a network-specific standard protocol. It is described in RFC 903. Some network hosts, such as a diskless workstation, do not know their own IP address when they are booted. To determine their own IP address, they use a mechanism similar to ARP, but now the hardware address of the host is the known parameter, and the IP address is the queried parameter.The reverse address resolution is performed the same way as the ARP address resolution. The same packet format is used for the ARP.An exception is the operation code field that now takes the ... Read More